Several questions re: parents' impending divorce....

I'm a 19 year old son who is soon (as in ASAP, yesterday if possible) to help my mother file for divorce. I've got a few questions...

To begin, I'll tell a quick history:
My parents have, as of this past week, been married for 27 years. During the first few years of their marriage, my father was physically abusive to my mother - this continued sporadically until I was around 6 years old, which I remember. She had not left him because she was financially unable, and feared the effects it could have on me. Until 1992, he worked and brought home a somewhat decent income, though it was not enough to purchase a house and we lived in a mobile home on land that my mother owned. That year, he was caught and convicted (as a felon) of drug use (methamphetamine, I believe). His job was immediately lost, but because of my mother then owning a small business where she needed him to continually perform maintenance on equipment, and the fact that they had a child, his sentencing was either 30 or 60 days in a county jail on weekends. He of course was not working, and my mother was forced to deplete the 401k and savings account.
He returned to work as a truck driver and no longer abused my mother because she had not left (she thought she would give him another chance, etc. etc., and she couldn't pay the bills on her own), and made decent money - enough, at least, to purchase a slightly larger, new home (still a manufactured, delivered one, which was of course socially detrimental to me). My grandfather (mother's father) died when I was 14, I believe - leaving my mother a small inheritance (something like $30k). My father began having months without work in the winter, and she had to help pay bills, which was something that she had not had to do in the past. She began working long hours when possible at different jobs to help financially, but he knew they could fall back onto her money if he didn't work. She also began having occasional odd rashes apparently at this time in her genital region, but they were very infrequent and she thought they were infections or something. She has -never- cheated.
I received a merit-based scholarship amounting to around $40,000 per year to my school (elite private university in Atlanta), which covers most things but still leaves me realistically needing another $6000 per year or so to cover food, clothes, books, etc. when not even including a car which I really do need to work. Once I was here, I knew that my mother had a close childhood friend nearby, and persuaded my mohter to finally leave my father, as the mortgage payments were falling behind and I saw that her money was going to be gone soon, because he was useless. He was not really supporting me in any manner at this time, either. We also know that he failed a drug test in trying to start a new job. I worked to sell the home, whcih finally happened before it was repossessed. My father, after much pleading, convinced us that he was willing to make it work. He moved here and they soon leased a home for one year (this happened last may). In July, he quit his job unexpectedly and layed in bed for 3 days. We found out that he was taking Ambian or some other pills of some sort, and thus literally forced him to leave, and so he moved back to his father's home in Alabama.
I should note that none of us have officially switched licenses, etc. to Georgia, and have used that grandfather's address for things like that. My father again began work and finally my mother allowed him to visit her, but not live here - he visited 4-5 times since this event, each time giving her a few hundred dollars, definitely not amounting to very much, and he has not given me money to pay for around $1200 in medical bills I've paid since December alone (I have crohn's disease and ADD, and have to pay monthly psychiatrist bills and medication bills for treatment). I now know that he has made around $26,000 since last summer (July), which does -not- explain his not giving us more money, especially given my needs. (Her income for the entire YEAR was $15,000, so she can't help me, though she's given me what he gave her) Three days ago, my mother went to a doctor regarding another occurance of the genital problems (sporadically for about 2-3 years now), and found that she has herpes. She has had sex with noone except my father in 27 years, and it's now obvious that he has cheated on her, likely at the time when she was having to pay all the bills and such.
She and I want a complete divorce as quickly as possible. He denied then quickly became offensive about the disease issue by phone, and has not called her back in three days. He lives in Alabama, she lives in Georgia (but still has alabama license, so I'm not sure about residency status). In addition to the $6,000 or so per year for just school-related expenses that I still need, I have car insurance that is of course very, very expensive and around $200 per month recurring medical expenses. I can go without neither, as I must work to help pay for them, and I need the ADD medication because I'm close to losing my scholarship, as I was not diagnosed until December when I could finally afford the testing, since my father had never paid for it, and I had several bad semesters GPA-wise. I know he will fight against paying anything for me, as we do not get along to begin with because of all the things he has done that have hurt me - financially, socially, and emotionally. We cannot afford significant legal fees, as it's taking -everything- my mother and I make just to get by the monthly expenses. Given that I'm 19 (20 on May 10th), can he be forced to pay child support? Also, my mother will now have large bills associated with her having contracted a disease, and is obviously significantly damaged emotionally and socially given that she has had it for 3 years and not known, and he never told her. Now she rather depressed, and I believe she needs therapy, which she cannot afford. I should also note that around $400/month of her income goes toward health insurance to cover her and me. She has asked him repeatedly (as have I) to provide health insurance for me, and he has not. We actually never even had health insurance until I was in college, so that's no big surprise.
What can we do? Please, give any and all recommendations as we're obviously weak financially and this can only get worse - he absolutely deserves to pay for at least my medical and school expenses now, but that doesn't even repay everything he has more or less caused to my mother and myself in the past, such as her inheritance dwindling to nothing because of his actions. Please just let me know anything you can.

Thank you so much!
-Garrett